FEN stands for "Forsyth-Edwards Notation", a standard for describing a chessboard in one line (thank you, Mr. Evans).

Here is the FEN for starting board position:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1

The first set of characters (before the first space) arranges the pieces on the board. White pieces are capital letters, while black are lowercase. Numbers represent blank empty squares.

The remaining characters describe who has the move, castling abilities, the target en passant square, half-move clock, and the fullmove number.

You need to install this font. or you will see only a confusing grid of mumbo-jumbo.